Fate of heterotrophic bacteria in Lake Tanganyika (East Africa)

Abstract

Bacterial mortality was studied using two complementary methods between 2002 and 2004 in the two main basins (north and south) of Lake Tanganyika. The disappearance of radioactivity from the DNA of natural assemblages of bacteria previously labeled with tritiated thymidine was used to estimate the mortality due to grazing by predators (72%) and due to the cell lysis (28%). Measurements of ingestion rate of bacteria by protozoa using fluorescent micro-particles yielded protozoan grazing rates similar to those provided by the thymidine method, and showed that heterotrophic nano-flagellates were responsible for most of the grazing pressure on the bacterial community of the pelagic zone (92-99%). Bacterial cell lysis was the second process involved in bacterial mortality, ranking before ciliate grazing. Overall, bacterial mortality was balanced with bacterial production. With regard to the assessment of the trophic role of bacteria, it was estimated that c. 5-8% of the organic carbon taken up by bacteria was converted into protozoan biomass and was thus available for metazoans.

Presence, abundance and bacterivory of the mixotrophic algae Pseudopedinella (Dictyochophyceae) in freshwater environments

“…The available values of CR (Nygaard & Tobiesen 1993, Havskum & Riemann 1996, the present study) range between 0.9 and 6.2 nl cell -1 h -1 . These rates of bacterivory are comparable to those observed for highly bacterivorous chrysophytes, like Dinobryon (see review by Unrein et al 2010) and Ochromonas (Sanders et al 1990, Epstein & Shiaris 1992, Callieri et al 2006, and for HF of similar cell size (Laybourn-Parry & Marshall 2003, Jezbera et al 2005, Pirlot et al 2007. Another indication of the relative importance of hetero trophic nutrition in Pseudopedinella spp.…”

Relationships between pelagic bacteria and phytoplankton abundances in contrasting tropical freshwaters

“…Recent studies have been carried out in tropical regions (Bouvy et al 1998, Canosa & Pinilla 2007, Pirlot et al 2007, Sarmento et al 2008, Stenuite et al 2009), but a comprehensive understanding of structural dependency between these aquatic communities is still required. Potentially, the tropics exhibit a large spectrum of types of aquatic ecosystems, especially freshwaters, i.e.…”

Differential Decay of Enterococci and Escherichia coli Originating from Two Fecal Pollution Sources

“…In general, the detrimental effect of sunlight is more pronounced in marine waters than in freshwater (12,16,20,21), while the opposite is the case for biotic interactions (22, 23). However, the majority of FIB decay studies use laboratory-grown control strains and conduct experiments under artificial conditions (18,(24)(25)(26)(27), which cannot accurately depict the behavior of FIB originating from "natural" sources and the complexity of interactions in aquatic ecosystems.The objective of this study was to investigate the effect of select environmental parameters, including (i) water type, (ii) exposure to ambient sunlight, and (iii) the presence of indigenous aquatic microbiota, on the viability (i.e., culturability by standard methods) of E. coli and enterococci originating from cattle manure or primary municipal wastewater effluent. Field-deployable submersible mesocosms allowed the assessment of environmental stressors on the decay of FIB by closely mimicking the release of these organisms into a recreational water body.…”

“…In general, the detrimental effect of sunlight is more pronounced in marine waters than in freshwater (12,16,20,21), while the opposite is the case for biotic interactions (22, 23). However, the majority of FIB decay studies use laboratory-grown control strains and conduct experiments under artificial conditions (18,(24)(25)(26)(27), which cannot accurately depict the behavior of FIB originating from "natural" sources and the complexity of interactions in aquatic ecosystems.…”